A number of catalytic systems have been examined for application to melt polycarbonates. Most of these methods require either a variety of co-catalysts or the subsequent addition of a catalyst quencher to ensure polymer stability. The need for high purity, high quality thermoplastic resins requires the reduction of residual contaminants in the final resin. This need for minimal residual impurities is particularly acute in optical quality (OQ) grade polycarbonate resins. One approach towards elimination of residual solvent contamination (particularly methylene chloride) implements a solventless (melt) process.
Most current melt technology programs employ a two component catalyst system. The first component is tetramethylammonium hydroxide (TMAH or .beta.-catalyst) which is used to initiate oligomer formation in the melt. The TMAH decomposes in the first two reactors to produce a variety of products, some of which contaminate the final polymer. The second catalyst is sodium hydroxide ("sodium" or Na; the .alpha.-catalyst) which is the finishing catalyst. Due to its intrinsic stability, the .alpha.-catalyst must be quenched. This quenching process requires the addition of yet another component to the polymer formulation. All the materials from the quenching process remain in the final resin, further contaminating the final polymer.
The use of a thermally stable, volatile tertiary amine catalyst circumvents the degradation problem of the .beta.-catalyst and the need for additional reagents due to the use of an .alpha.-catalyst. Volatile amines provide the advantage of being "self-quenching" i.e., these catalysts slowly distill from the resin over the course of the reaction. As a result, no additional quencher is needed and no detrimental catalyst residue is left in the final resin.